In various technical fields, CRTs (Cathode Ray Tubes) have gradually been replaced by hold-type display apparatuses including a liquid crystal display module or an EL display module.
It is considered, however, that hold-type display apparatuses are inferior in moving image qualities to impulse-type display apparatuses such as CRTs (Cathode Ray Tubes) in which a turn-on time during which an image is displayed and a turn-off time during which an image is not displayed are alternated.
That is to say, in a typical hold-type display apparatus, a whole one frame period is an image turn-on time. On this account, once a frame image is updated, an object is being displayed until the image is updated in the next frame, and the image displayed in this way appears as motion blur for the viewer.
To achieve improvement in the moving image quality as one of the objectives, various methods have been proposed to perform driving in such a way as to time-divide a single frame for displaying one image into plural sub frames. An example of such methods is disclosed by Patent Document 1. It is noted that image display apparatuses adopting organic LED panels have been arranged so that vertical scanning is multiplexed.
Among hold-type display apparatuses, liquid crystal display apparatuses are disadvantageous in that the electro-optical properties of the liquid crystal are deteriorated when a unidirectional electric field is applied thereto over a long period of time. The liquid crystal display apparatuses are typically driven on AC in order to prevent the deterioration of the liquid crystal. In other words, the driving is typically performed such that the polarity of the voltage applied to each pixel is alternated.
Examples of the AC driving methods for applying a voltage to each pixel are as follows.
The polarity of voltages applied to respective pixels neighbored in the horizontal direction (the direction along the scanning signal lines) are differentiated, and the voltages applied to the pixels are reversed in each frame (line inversion driving).
The polarities of the voltages applied to the respective pixels neighbored in the vertical direction (the direction along the data signal lines) are differentiated (i.e. the polarity of the voltage applied to the pixels on a scanning signal line is reversed each time a different scanning signal line is scanned), and the voltage applied to each pixel is inverted.
The polarity of the voltage applied to a pixel is differentiated from the polarity of the voltages applied to the pixels which neighbor that pixel in the horizontal and vertical directions, and the voltage applied to each pixel is inverted in each frame (dot inversion driving).
FIG. 15(a) illustrates the polarity of the grayscale display voltage applied to each pixel in a conventional liquid crystal display apparatus performing the dot inversion driving. FIG. 15(b) is a timing chart showing the relationship between the grayscale display voltages applied to the respective pixels and time.
As shown in FIG. 15(a), in case of the dot inversion driving, the polarities of the grayscale display voltages applied to the horizontally-neighbored pixels are different, and the polarities of the grayscale display voltages applied to the vertically-neighbored pixels are also different. Furthermore, as shown in FIG. 15(b), the polarity of the grayscale display voltage is inverted in each frame.
The AC driving, however, is arranged such that, when the polarity of the voltage (grayscale display voltage) applied to each pixel is reversed, a data signal line drive circuit discharges the electric charge on the data signal lines and the pixel capacities by injecting the electric charge with the reverse polarity, and then the data signal line drive circuit is charged up to a desired grayscale display voltage. Because of this arrangement, the AC driving is disadvantageous in that the power consumption for the driving is large.
To solve this problem, for example, Patent Document 2 discloses a source driver which is arranged as follows. The source driver alternates an output signal from an odd-number-th output section of the source driver between a high voltage level and a low voltage level and switches an output voltage supplied from an even-number-th output section in the order in reverse to the odd-number-th output section. In the source driver, a first share line connected to each odd-number-th output section via a switch and a second share line connected to each even-number-th output section via a switch are charged to certain voltage levels, respectively. Before a voltage output from the source driver to an output section is switched between the high voltage level and the low voltage level, the output section is connected to the first or second share line, so that the capacitor of the panel is arranged to be constant.
In other words, in the technology disclosed in Patent Document 2, before the switching of an output voltage supplied to each output section between the high voltage level and the low voltage level, each output section is charged with a constant voltage which has been supplied to the first or second share line. Therefore, the source driver is only required to charge, with the grayscale display voltage, a data line which has already been charged with a certain voltage (of the first or second share line), and hence the power consumption in this case is small as compared to a case where a grayscale display voltage of a low voltage level is charged to a line which has been charged at a high voltage level and a case where a grayscale display voltage of a high voltage level is charged to a line which has been charged at a low voltage level. The technology of Patent Document 2, however, requires to charge the first and second share lines at certain voltages in advance.
Patent Document 3 teaches that output terminals are short-circuited in a blanking period, in a liquid crystal driving apparatus which has plural output terminals which output driving signals to a liquid crystal panel in such a manner that neighboring output terminals output driving signals having inverse polarities, and the polarity of a driving signal output from a single output terminal is inversed in each scanning period.
In other words, in Patent Document 3, for the dot inversion driving, output terminals are short-circuited so that the output terminals have the same electric potential, in a blanking period before the switching of the polarity of each output terminal. As a result of this, the electric potentials of the output terminals, which potentials are identical with one another, are close to the electric potentials after the polarity inversion, and hence the power consumption is small as compared to a case where an electric potential in the previous scanning period is changed to the electric potential with the inverse polarity.
[Patent Document 1]
Japanese Laid-Open Patent Application No. 2005-173573 (published on Jun. 30, 2005)
[Patent Document 2]
Japanese Laid-Open Patent Application No. 2003-228353 (published on Aug. 15, 2003)
[Patent Document 3]
Japanese Laid-Open Patent Application No. 9-212137/1997 (published on Aug. 15, 1997)